Sistant objects manufactured from this hard metal method for preparing hard metal based on titanium carbide and wear re

ABSTRACT

THE INVENTION RELATES TO A METHOD FOR PREPARING A HARD METAL BASED ON TITANIUM CARBIDE, WHEREIN A MIXTURE OF TITANIUM CARBIDE POWDER AND AT LEAST FOUR PERCENT BY WEIGHT OF TITANIUM NICKEL POWDER IS GROUND AND THE GROUND BLEND OF TIC AND TINI IS SINTERED FOR AT LEAST THREE MINUTES UNDER VACUUM OR AN INERT GASEOUS ATMOSPHERE AND UNDER A MECHANICAL PRESSURE OF AT LEAST 150 KG/CM.2 AT A TEMPERATURE THAT LIES ABOVE 1315*C., THE MELTING-POINT OF TINI.

p 1973 R. G. DE LANGE ETAL 3.7559787 METHOD FOR l'lilfilARlNG HARD METAL BASED ON TlTANIUM CARBIDE AND WEAR RESISTANT OBJECTS MANUFACTURED FROM THIS HARD METAL Filed Nov. 15, 1971 aooo T '-r*. mln. g max.

so 0 F 1p 2p an 49 so INVENTOR.

ROBERT G. DE LANGE JACOBUS A. ZIJ'DERVELD BY GERARDUS A. VAN KUPPEVE yzwwi, Li 2214,

3,756,787 Patented Sept. 4, 1973 3,756,787 METHOD FOR PREPARING HARD METAL BASED ON TITANIUM CARBIDE AND WEAR RESIST- ANT OBJECTS MANUFACTURED FROM THIS HARD METAL Robert Gerardus De Lange, Vlaardingen, Jacobus Antonius Zijderveld, Waddinxveen, and Gerardus Antonius Van Kuppevelt, Delft, Netherlands, assignors to Ncderlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Ten Behoeve Van Nijverheid, Handel En Verkeer, Hague, Netherlands Filed Nov. 15, 1971, Ser. No. 198,820 Claims priority, application Netherlands, Nov. 20, 1970, 7016999 Int. Cl. B22f 1/00 US. Cl. 29-182.8 Claims ABSTRACT OF THE DISCLOSURE The invention relates to a method for preparing a hard metal based on titanium carbide, wherein a mixture of titanium carbide powder and at least four percent by weight of titanium nickel powder is ground and the ground blend of TiC and TiNi is sintered for at least three minutes under vacuum or an inert gaseous atmosphere and under a mechanical pressure of at least 150 kg./cm. at a temperature that lies above 1315 C., the melting-point of TiNi.

The invention relates to a method for preparing a hard metal based on titanium carbide and to wear-resistant objects manufactured from this hard metal such as tools, cutting tools, punches, drawing dies, dies, warheads and similar objects.

It is known in the art that for the preparation of hard metal based on titanium carbide nickel is applied as a bonding agent and a percentage of molybdenum or molybdenum carbide is added. This may give rise to formation of multicarbides and is necessary for achieving a good quality. When there is no such addition the insuflicient shock-resistance makes the use of this hard metal as tool or cutting tool hardly possible.

It is the object of the invention to provide an improvement of the hard metal based on titanium carbide without the addition of molybdenum or molybdenum carbide.

Therefore no nickel is used as a bonding agent but according to the invention a mixture of titanium carbide powder and at least four percent by weight of titanium nickel are ground and the ground mixture of TiC and TiNi is sintered for at least three minutes under vacuum higher than 0.1 mm. Hg at a temperature of at least 1315 C., the melting point of TiNi, under a mechanical pressure of at least 150 kg./cm.

According to the invention a percentage of from 4 to 30 of TiNi is applied with 54 to 61.9 percent by weight of nickel and preferably 520% of TiNi and a sinter temperature of 1315 C. to 1430 C. is taken, preferably between 1375" C. and 1400 C., for a period of time of 3 to 40 minutes, preferably -30 minutes. The amounts of TiNi have been chosen such that in the object made the bonding agent will mainly consist of the ductile compound T iNi and that the formation of intermetallic compounds of the type of Ti Ni on the one hand and of TiNi on the other hand will be avoided as much as possible.

According to the invention the mixture of the powders of titanium carbide and titanium nickel is preferably obtained by grinding for l to 100 hours in a ball mill a titanium carbide powder with a grain size of less than 20 microns together with a nickel titanium powder with a grain size of less than 50, under protection of an organic liquid such as pentane, into a homogeneous mixture. The grain size of the sintered object then is below 10 microns.

Grinding is carried out under a protective liquid in order to check oxidation and dusting. Low-boiling liquids are applied because after grinding these evaporate from the mixture automatically or at somewhat increased temperature. Low-boiling hydrocarbons, e.g. pentane and hexane but also chlorinated hydrocarbons such as trichlo roethylene or acetone are satisfactory. Pentane was found to be very suitable. The ground powder as such can be compressed and sintered according to the invention without intermediate shaping and consequently the use of bonding agents is superfluous.

The invention is further described and elucidated below with reference to the results of machining tests with throw-away tips obtained according to the invention and throw-away tips known in the art with reference to a graph, in which the wear of the relief face is plotted against the course of the tool.

As base material the titanium carbide is applied, which is easier to obtain than tungsten carbide and after sintering possesses a greater hardness, resistance against crater wear and oxidation resistance. The grain size of the titanium carbide that is started from lies between 3 and 20 microns. As a bonding agent the intermetallic compound TiNi is applied, which combines a high strength with a great ductility and corrosion resistance. The grain size of the titanium nickel lies between 4 and 50 microns and the intermetallic compound TiNi contains between 54 and 61.9 percent by weight of nickel at a temperature lower than the melting point of 1315 C. In order to guarantee a sufficient hardness of the hard metal not more than 30 percent by weight of TiNi is applied, whereas a minimum of approximately four percent by weight is necessary to ensure a sufiicient bonding between the titanium carbide grains after sintering.

The mixture of the two powders is ground in a hardmetal ball mill under protection of an organic liquid such as pentane, hexane, acetone, trichloroethylene but preferably pentane, into a grain size of preferably less than 1 micron. If coarse grains are started from, the grinding period increases, possibly more than hours, but with finely granulated grains the grinding period can be reduced to less than 10 hours. In the event of a quantity of more than 10% TiNi grinding must be longer continued due to the ductility of the bonding agent and must be effected for at least 24 hours. In the event of higher percentages of bonding agent after sintering the compressive strength of the object obtained drops in respect of that at lower percentages of bonding agent. Upon grinding a thorough blending of base material and bonding agent is effected, the hard titanium carbide grains being enveloped as it were by TiNi.

The ground powder blend is dried by contact with air and the organic liquid evaporates. Then the blend is trans ferred to a die preferably of graphite of the dimensions desired. In this die the blend is compressed, while the whole is brought under a vacuum higher than 0.1 mm. Hg and the temperature is raised to above 1315 C. Upon exceeding the melting point of TiNi a liquidus solidus system is created, the solid titanium carbides being taken up into the titanium nickel and sintering of liquid being elfected with a considerable densification. The pressure is raised to at least kg./cm. and when graphite dies are used up to maximum 250 kg./cm. in order to obtain a greater density with, correspondingly, an improvement of the heat conductivity, the modulus of elasticity and the tensile and compressive strengths. The external pressure must be great as compared with the surface tension between the titanium nickel and the titanium carbide, in order to obtain an adequate wetting. The amount of TiNi must not be too large, preferably under 20%, because otherwise forcing out of the liquid titanium nickel occurs and contamination with the die material may occur. The densification lowers with time, so that a sintering time longer than 40 minutes is superfluous. Moreover, a longer sintering, time involves the risk of a considerable diffusion of the titanium and hence secondary growth of grains with the chance of brittle compounds occurring such as Ti Ni and TiNi Preferably sintering is not continued beyond 30 minutes at a temperature that lies under 1400 C. and above 1375" C. The higher the temperature and the pressure are chosen, the shorter the sintering time can become. The sintering time must not lie below 3 minutes, however, because otherwise no suflicient densification is effected, and furthermore, a lower limit of 150 kg. /cm. is necessary. Therefore, sintering is preferably effected at a temperature of 1380 C. 'and a pressure of 200 kg./cm. longer than 10 minutes.

After sintering has been completed, cooling is effected and the mechanical pressure is reduced, whereupon the object obtained is lifted out of the die. Instead of under vacuum the process can also be carried out under an inert gaseous atmosphere.

An example of the method according to the invention is the following:

A mixture of '95 percent by weight of TiC powder (grain size 4 to 6 microns, supplier Starck B.R.D.) and 5 percent by weight of powder of the intermetallic compound TiNi (grain size 5 to 30 microns, supplier Alfa Inorganics USA.) is ground for 24 hours in a hard-metal ball mill (make Fritsch Pulverisette type 601) under protection of pentane. After grinding the pentane is removed from the mixture by evaporation at room temperature.

The powder blend is transferred to a graphite die of the dimensions desired, for example 14 x 14 mm. square.

Densification of the powder is effected by pressure sintering in a sintering press (make Degussa type VSpgr 5/10) under the following conditions: minutes heating up time up to a sintering temperature of 13 80 C., a sintering time of minutes under a compressive force of 200 kg./cm. and a vacuum higher than 0.1 mm. Hg.

approximately 30 minutes under these conditions and the other two for approximately 21 minutes.

When tested under extreme machining conditions with a circumferential speed of 450 mtr./min., a feed of 0.3 mm./rev. and a depth of cut of 2.5 mm. on the same material a throw-away tip according to the invention displayed only a slight crater wear. The PlO-SI tip displayed a substantial crater after 48 seconds already, whereupon chipping off of the cutting edge would have occurred and the tool would have to be written off. A VR65P01 tip displayed a clear wear spot after 3 minutes and after 8 minutes the cutting edge had a serious wear slit, while due to the serious wear the depth of cut had already decreased until 2 mm.

In order to obtain still another comparison with a throw-away tip out of a hard metal based on TiC and known in the art, tips of D-12-U-304-LT2 of Sintronic were compared with those according to the invention. All tips measured 12.7 x 12.7 x 4.8 mm. and had been arranged under a true rake angle of 6 degrees, a relief angle of 5 degrees, a back rake angle of 0 degrees, a side cutting-edge angle of 20 degrees and a nose radius of 0.4 mm., while the nose radius and the relief faces had been re-ground. Of each make three tips were tested with a cutting speed of 300 m./min., a feed of 0.16 mm./rev. and a depth of cut of 0.8 mm., here, too, on an unalloyed heat-milled constructional steel with a strength of 60-70 kg./mm. The progress of the wear of the relief face over a certain tool course was chosen as standard of comparison. Tips S1, S2 and S3 were of Sintronic and tips T1, T2 and T3 had been prepared according to the invention.

In the table the various values of the wear of the relief face have been expressed in 0.01 mm. and the table has been further detailed in the graph with on the base the wear of the relief face and on the vertical the tool course covered in meters. The average of the three values given in the table is indicated in the graph by gem.

TABLE Wear of the relief face in 0.01 mm.

Tool course in m 500 1,000 1, 500 2,000 3,000 5, 500 6, 500 8,000 9,000

Sintronic average,

Plate T1. 6 8 10 10 11 17 18 25 25) Plate T 17 17 17 18 20 29 29 32 30 Plate T 12 14 14 16 16 26 27 31 36 'lNO average, T1,

The grain size of the sintered carbide amounts to 18 microns.

The object thus obtained has a high hardness (1850 V.P.H.), a reasonably high bending strength (80 kgf./ mm?), a compressive strength (268 kg/mm?) and a particularly good machinability. The properties are considerably better than those of the hard metal types based on TiC and known in the art which is seen from the following experiments.

Out of a hard metal based on TiC and with 5% of TiNi and prepared according to the invention throw-away tips were made, which were subjected to comparative tests, along with other cutting materials known in the art such as P10-SI of A. E. E. MERK with 26% of (TiC-i-TlaC),

9% of Co, balance TC and VR-65-P01 of Vr-Wesson with 75% of TiC and 25% of (NiC+MoC). The machining conditions were: a circumferential speed of 320 mtr./ min., a feed of 0.07 mm./rev. and a depth of cut of 0.25 mm. on an unalloyed heat-milled constructional steel with a strength of -70 kg./mm. The throw-away tips according to the invention were found to be utilizable for From the table and from the graph it appears that on an average the various values of the wear of the relief face for the tips according to the invention are 30% lower than those of the other tips. Up to a tool course of 3000 meters the wear of the tips according to the invention hardly increases and only between 6500 and 8000 meters it becomes equal to the wear that has been reached already after 3000 meters for the tips known in the art. In particular after 2000 meters for the tips known in the art a considerable rise occurs. This means that on maintaining a certain precision of the work piece the life of the tips according to the invention is more than twice that of the tips known in the art. Owing to the better properties the hard metal prepared according to the invention is not only suitable for machining tools, but also for punches, dies and drawing dies. Moreover, it can be used for warheads that must have a great hardness and penetrating power as compared with panzer material.

We claim:

1. A method for preparing a hard metal based on titanium carbide, wherein a mixture of titanium carbide powder and at least four percent by weight of titanium nickel powder containing from 54% to 61.9% of nickel is ground and the ground blend of TiC and TiNi is sintered for at least three minutes under vacuum or an inert gaseous atmosphere and under a mechanical pressure of at least 150 kg./cm. at a temperature that lies above 1315 C., the melting-point of TiNi.

2. A method according to claim 1, wherein application is made of up to thirty percent by weight of titanium nickel, and maximum for 40 minutes a sintering temperature to 1430 C. and a mechanical pressure to 250 kg./ cm

3. A method according to claim 1, wherein for to minutes a percentage of from 5 to 20 of titanium nickel is applied and a sintering temperature of from 1375 C. to 1400 C. under a mechanical pressure of 200 kgJcmF.

4. A method according to claim 1, wherein a titanium carbide powder of a grain size of less than 20 microns together with a titanium nickel powder of a grain size less than microns is ground under protection of an organic liquid such as pentane, hexane, acetone, trichloroethylene and the like for at least 10 hours and possibly 100 hours into a homogeneous blend.

6 5. A metal article obtained according to the method of claim 1.

References Cited BENJAMIN R. PADGE'IT, Primary Examiner B, HUNT, Assistant Examiner US. Cl. X.R. 

